WO2012042150A1

WO2012042150A1 - Method of managing the priority of preliminary media streams

Info

Publication number: WO2012042150A1
Application number: PCT/FR2011/052173
Authority: WO
Inventors: Jean-Claude Le Rouzic; José DOREE
Original assignee: France Telecom
Priority date: 2010-09-30
Filing date: 2011-09-21
Publication date: 2012-04-05
Also published as: FR2965690A1

Abstract

Method for managing the priority of preliminary media streams. This method may be implemented by a called terminal in an IMS network. It comprises: - a step (E10) of receiving an SIP invite message emitted by a calling terminal so as to establish a communication between said terminals; - prior to a possible establishment of said communication, a step (E30) of dispatching an SIP response of type 18x intended to inform said calling terminal that said called terminal has been alerted, said response comprising an SDP message comprising characteristics of a preliminary media stream liable to be established between said calling terminal and said called terminal before the establishment of said communication; and - a step (E20) of inserting, into said SIP response, an indicator (IND) of priority of said preliminary media stream.

Description

METHOD FOR MANAGING THE PRIORITY OF PRELIMINARY MEDIA STREAMS

Background of the invention

The present invention is in the field of IMS (IP Multimedia Subsystem) type telecommunications networks as defined by the 3GPP (Third Generation Partnership Project).

The invention is more particularly in the context of the media streams (eg audio or video) that can be exchanged between a calling terminal and a called terminal during the call establishment phase, ie before the establishment of the call, such streams being known to those skilled in the art as "early media", hereinafter referred to as "preliminary media streams".

Thus, in this document, the terminology "preliminary media flow" or "early media" will designate any multimedia flow exchanged between the issuing of the invitation message INVITE by the calling terminal and the sending of the final response type 200 OK by the terminal called for the establishment of the call.

For example, the preliminary media streams may be used to convey a Call Returned Call (CRBT) signal or an announcement message to the caller.

In addition, since several terminals may have the same public IPU (IP Multimedia Public Identity) identity, the IETF document RFC3261 defines a mechanism for ringing, in the event of an incoming call destined for a given public identity IMPU, one or more terminals having this same public identity IMPU since they are registered at the heart of network IMS.

More specifically, when an incoming call to an IMPU identity is presented to the Serving Call Session Control Function (S-CSCF) server, a so-called "forking" module of this server generates an INVITE invitation message at destination. each of the terminals concerned, either sequentially or in parallel.

Each of the called terminals receiving this INVITE invitation message is likely to attempt to establish a preliminary media stream with the calling terminal.

In the current state of the art, the processing of these competing flows depends on the implementation chosen by the manufacturer of the calling terminal. The chosen policy generally consists in rendering the first or the last preliminary media stream received by the terminal. From the point of view of the operator, this results in arbitrary and heterogeneous behaviors preventing the establishment of satisfactory service logic. Object and summary of the invention

According to a first aspect, the invention relates to a first method implemented by a called terminal in an IMS network, this method comprising:

a step of receiving an INVITE SIP message sent by a calling terminal to establish a communication between these terminals; and

prior to eventual establishment of the call, a step of sending a SIP response type 18x intended to inform the calling terminal that the called terminal has been alerted, this response comprising an SDP message comprising characteristics of a flow preliminary media likely to be established between the calling terminal and the called terminal before the establishment of the call.

This first method comprises a step of insertion, in the SIP response, of a priority indicator of the preliminary media stream.

Correlatively, the invention relates to a first device that can be integrated in a first terminal, this device comprising:

means for receiving an INVITE SIP message sent by a calling terminal to establish a communication between these terminals; and

means for sending, beforehand to a possible establishment of the call, a SIP response of the type 18x intended to inform the calling terminal that the first terminal has been alerted, this response comprising an SDP message including characteristics of a preliminary media stream capable of to be established between the calling terminal and the first terminal before the establishment of the call.

This first device comprises means for inserting, in the SIP response, a priority indicator of the preliminary media stream.

This first aspect of the invention therefore relates to the operations performed by the called terminal, wishing to establish a preliminary media flow with the calling terminal.

According to a second aspect, the invention relates to a method for processing an 18x type SIP response sent by a called terminal to a calling terminal, this response comprising an SDP message comprising characteristics of a preliminary media stream capable of to be established between the calling terminal and the terminal called before the establishment of a communication between these terminals. This process comprises:

a step of obtaining, in the SIP response, a preliminary flow priority indicator; and

a decision step concerning the authorization, blocking or suspension of the preliminary flow report by the calling terminal according to this priority indicator.

Correlatively, the invention relates to a device for processing a SIP response of the type 18x sent by a called terminal to a calling terminal, this response comprising an SDP message comprising characteristics of a preliminary media stream that can be established between the calling terminal and the called terminal before establishing a communication between these terminals.

This second device comprises:

means for obtaining, in the SIP response, a priority indicator of the preliminary media stream; and

means for making a decision as to the authorization, blocking or suspension of the rendering of the preliminary media stream for the calling terminal according to the priority indicator.

This second aspect of the invention relates to the operations performed by the equipment or devices responsible for controlling the reproduction of the preliminary media stream by the calling terminal.

Thus, in general, the invention proposes to insert, in the SIP response type 18x, a priority indicator relative to each of the proposed responses in call establishment phase.

The management of this indicator is the responsibility of the processing device according to the invention.

The devices according to the invention can be integrated in different types of equipment of the network.

First, the first device, capable of inserting into the SIP response a priority indicator of the preliminary media stream can be incorporated into various equipment.

Therefore, the invention is directed to a terminal (terminal called directly or by forking) and an application server ("application server", or AS, in English) comprising a first device as mentioned above.

The device for processing a SIP response according to the invention can also be incorporated in various equipment of the telecommunication network. There are two main variants of implementation of this second aspect of the invention.

In a first variant, the device for processing a SIP response is incorporated in a device having both a visibility on the signaling plane and on the media plane.

In this variant embodiment, the equipment incorporating the first device according to the invention can, by itself, start, stop or suspend the reproduction of the preliminary media stream by the terminal as a function of the decision taken by this device.

This equipment may for example be constituted by the calling terminal itself, or by an edge entity SBC.

Therefore, the invention also provides a terminal comprising:

means for sending an INVITE SIP message to a called terminal, this message being intended to establish a communication between these terminals;

means for receiving a type 18x SIP response transmitted by the called terminal, this response comprising an SDP message comprising characteristics of a preliminary media stream that can be established between these terminals before establishing communication between these terminals. This terminal comprises a first device for processing the SIP response as mentioned above; and

control means capable of starting, stopping or suspending the rendering of the preliminary media stream by the terminal as a function of the decision made by this first device.

The invention also relates to an entity that can be placed in a flow-off between a calling terminal and a called terminal in an IMS network, this entity comprising:

means for receiving a type 18x SIP response sent by the called terminal to the calling terminal, this response comprising an SDP message comprising characteristics of a preliminary media stream that can be established between said terminals before the establishing communication between these terminals.

This entity comprises:

a second device for processing the SIP response as mentioned above; and

control means able to start, stop or suspend the rendering of a preliminary media stream by the calling terminal according to the decision made by this first device. This entity may for example be constituted by an edge entity (SBC) at the boundary between an access network to which the calling terminal is connected to the IMS core network.

In a second variant embodiment of the invention, the second device for processing a SIP response according to the invention is incorporated into an equipment having only visibility on the signaling plane.

This equipment can be an application server AS placed in a flow cut between the caller and the called party and able to modify, if necessary, the value of the priority indicator of a preliminary media stream according to a logic of predetermined service. Such a service logic, implemented in the signaling plan, can notably be implemented in an application server of Originating or Terminating type.

This equipment having only visibility on the signaling plane can also, for example, be a P-CSCF server, an IBCF or an MGCF.

In this case, the equipment incorporating the device according to the invention sends a command to an entity having a visibility in the media plan for it to start, stop or suspend the restitution of the preliminary media stream by the calling terminal as a function of the decision taken by the device according to the invention.

Thus, in a particular embodiment, the device for processing a SIP response is integrated in a P-CSCF server, the latter being able to send a command to a C-BGF entity for it to control the flow. preliminary media according to the decision taken by the device according to the invention.

In two other embodiments of this second variant, the processing device can be integrated in an IBCF entity able to send a command to an I-BGF entity, or in an MGCF entity able to send a command to a TGW entity.

Preferentially, for a given set of preliminary media flows, the priority order of each of the responses to the SDP offers is unique.

It is the responsibility of entities or servers incorporating the second device according to the invention to manage the uniqueness of the proposed priorities in these responses for competing media streams. Very advantageously, on receiving the priority indicators, these entities or servers will ensure that only the highest priority preliminary media stream passes.

In one embodiment, concurrent media streams, i.e. of the same priority, may be allowed to be simultaneously retrieved by the calling terminal. In another embodiment, certain network devices may prevent the rendering of competing preliminary media streams, by blocking or suspending the rendering of a preliminary media stream when another preliminary media stream of the same priority is present. By way of non-limiting example, an operator may choose to restore the first or the last multimedia preliminary stream (policy of the first or last served).

The invention also relates to a signal intended to be transmitted by a terminal to a calling terminal in an IMS network, this signal carrying a SIP 18x response intended to inform the calling terminal that the called terminal has been called. alerted, this response comprising an SDP message having characteristics of a preliminary media stream that can be established between the calling terminal and the called terminal before the communication is established.

According to the invention, in this signal, the SIP response includes a priority indicator of the preliminary media stream.

From a protocol point of view, different solutions can be implemented to implement the invention.

In a first embodiment, the priority indicator is included in a header (in English "Header") of the SIP response reserved for this purpose.

In another embodiment, the priority indicator is a parameter of the P-EARLY-MEDIA header defined by the IETF RFC5009.

In a particular embodiment, the different steps of the first method and / or method of processing a SIP response are determined by computer program instructions.

Consequently, the invention also relates to a computer program on an information medium, this program being capable of being implemented by a computer, this program comprising instructions adapted to the implementation of the steps of the either of the methods as mentioned above.

This program can use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code, such as in a partially compiled form, or in any other form desirable shape.

The invention also relates to a computer-readable information medium, comprising instructions of a computer program as mentioned above.

The information carrier may be any entity or device capable of storing the program. For example, the medium may include storage means, such as a ROM, for example a CD ROM or a circuit ROM microelectronics, or a magnetic recording means, for example a diskette (floppy disk) or a hard disk.

On the other hand, the information medium may be a transmissible medium such as an electrical or optical signal, which may be conveyed via an electrical or optical cable, by radio or by other means. The program according to the invention can be downloaded in particular on an Internet type network.

Alternatively, the information carrier may be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the method in question.

Brief description of the drawings

Other features and advantages of the invention will emerge from the description given below with reference to the accompanying drawings which illustrate an embodiment having no limiting character.

In the figures:

Figure 1 shows a network in which the invention can be applied;

Figure 2 shows, in flowchart form, the main steps of a method according to the first aspect of the invention, in a particular embodiment of the invention;

Figure 3 schematically shows a SIP response message according to the invention, detailed examples of such a message being given in Annexes 1 and 2;

Figure 4 shows a signal according to the invention;

FIG. 5 represents, in flowchart form, the main steps of a method of processing a SIP response according to a particular embodiment of the invention;

Figure 6 shows a first terminal according to the invention;

Figure 7 shows a device for processing a SIP response according to the invention;

Figure 8 shows a second terminal according to the invention;

Figure 9 shows an edge entity according to the invention; and Figure 10 shows a P-CSCF server according to the invention. Detailed description of the invention

FIG. 1 represents an IMS network in which the invention can be applied.

In this figure, there is shown firstly the core IMS network 40 and an access network 41 in which there is a terminal A.

An SBC border entity 51 is placed at the boundary between the access network 41 and the IMS core network 40.

Other terminals B, C, D are connected behind another SBC border entity 58 at the edge of the IMS core network 40.

The terminals A, B, C, D can be connected directly to the access network, or be connected to the access network via a residential gateway.

In a known manner, the network of FIG. 1 makes it possible to establish communications and preliminary media flows (early media) between the terminals of the network.

In this example, it will be assumed that the terminal A is a calling terminal and that the other terminals are called terminals.

The IMS core network 40 comprises elements known to those skilled in the art, namely:

- P-CSCF servers 52, 57;

- S-CSCF servers 54, 56;

an I-CSCF server 55; and

- a C-BGF 53 entity.

For more information on these equipment, the skilled person can refer to the document TISPAN TS 123 517.

The SBC entities 51, 58 are border devices able firstly to control the SIP signaling and secondly to control the dynamic opening and closing of the media flows between the terminals.

The P-CSCF entity 52, placed in a flow cut between the calling terminal A and the other terminals, sees the SIP signaling and in particular the SIP type 18x responses sent by a terminal called B, C, D to the terminal. A to solicit the opening of a preliminary media flow (early media).

The C-BGF entity is at the media plane level and allows or not media streams to pass, depending on the commands it receives from the P-CSCF 52. The C-BGF does not see the signaling messages.

FIG. 1 also shows a terminating AS application server, in association with an MRF multimedia resource server. It is now assumed that the terminal A sends an INVITE invitation message to the terminal B to establish a multimedia communication.

In known manner, the response to such an invitation message is a SIP message type 18x, for example a message RINGING 180.

When the called terminal wishes to establish a preliminary media flow (early media) with the calling terminal, the SIP 18x response message includes an SDP message defining the characteristics of the preliminary media stream concerned.

We will assume that the called terminal B wishes to establish a preliminary media stream with the terminal A.

He then implements the method according to the first aspect of the invention, the main stages of which are represented in FIG.

After receiving the INVITE invitation request sent by the terminal A (step E10), the terminal B inserts, in the SIP response REP message 18x, an IND indicator of the priority of the preliminary multimedia stream that it wishes to transmit (step E20).

The SIP answer REP message is sent by the terminal B to the calling terminal A during a step E30.

FIG. 3 is a schematic representation of the 18x SIP response REP message sent by the terminal B.

This message comprises the IND indicator of the preliminary media stream and the SDP MSDP message defining the characteristics of this stream.

This response message can be transmitted in the form of a GIS signal according to the invention as shown in FIG. 4.

Upon receipt of this message, REP terminal A implements the method according to the second aspect of the invention and whose main steps are shown in Figure 5.

During a step F10 of this method, the terminal A obtains, in the 18x SIP response REP message, the priority indicator IND of the preliminary media stream that the terminal B wishes to establish.

Then, it takes, during a step F20, a decision as to the authorization, blocking, or suspension of the restitution of this preliminary media stream by the terminal A according to this priority indicator.

In the embodiment described here, several cases may occur:

when a new preliminary media stream is not in competition with any other preliminary media stream received by the terminal A, the terminal A directly renders this new stream; if the terminal A is already rendering a preliminary multimedia stream of higher priority than that of the new stream, then the new stream is rejected or put on hold until the end of the restitution of the current stream; and

if the new preliminary media stream is of higher priority than the other preliminary media streams received by the terminal A, then this new stream is restored, even if it interrupts or blocks the broadcasting of a preliminary multimedia stream of lower priority.

FIG. 6 schematically represents the hardware architecture of terminal B according to the invention.

This terminal B comprises a device 100 according to the invention. In the embodiment described here, this device 100 has the hardware architecture of a computer. It comprises a processor 101, a RAM RAM 102, a ROM ROM 103 and communication means 104.

The read-only ROM ROM 103 constitutes a support according to the invention in which a computer program PG1 according to the invention is recorded. This computer program includes instructions for implementing the method of FIG. 2 when these are executed by the processor 101.

These calculation means 101, 102 and 103 are particularly capable of inserting, in a SIP response type 18x, an indicator of the priority of a preliminary media stream.

The communication means 104 are able to receive a SIP message

INVITE from a calling terminal and send the SIP response to that terminal.

FIG. 7 represents a device 200 for processing a SIP response according to a particular embodiment of the invention.

This device 200 comprises a processor 201, a random access memory RAM 202 and a read-only memory type ROM 203.

The ROM-type ROM 203 constitutes a recording medium in accordance with the invention on which is recorded a computer program PG2 capable of implementing the method of processing a SIP response whose main steps have been previously described. with reference to FIG.

The computing means 201, 202 and 203 are particularly capable of obtaining, in a SIP response, a priority indicator of a preliminary media stream and to take a decision as to the authorization to block or suspend the return of that media stream. preliminary media stream by the calling terminal according to its priority indicators.

FIG. 8 represents the terminal A in accordance with the invention, this latter comprising a device 200 such as that described with reference to FIG. 7 and communication means 204. It will be noted in the example of FIG. 8 that the computing means (RAM processor, ROM memory of the terminal A) are those of the device 200.

In the embodiment that has just been described, the processing of a SIP response according to the invention is implemented by the calling terminal A.

FIG. 9 represents a border entity 51 according to the invention, this entity being able to implement the method of processing a SIP response of 18x type according to the invention.

This border entity 51 is placed at the boundary between the access network 41 in which the calling terminal A is located and the IMS core network 40.

In the embodiment described here, the border entity 51 presents the hardware architecture of the computer. It comprises a memory processor 501, a random access memory 502, a ROM ROM 503 and communication means 504.

These means 501, 502, 503 and 504 make it possible to perform the conventional functions of a border entity according to the current state of the art.

According to the invention, this edge entity 501 further comprises a device 200 able to process a SIP response of type 18x according to the invention as described above with reference to FIG. 7.

The processor 501, the random access memory 502 and the read-only memory 503 constitute control means for the border entity 51, these means being able to start, stop or suspend the restitution of the preliminary media stream by the terminal A as a function of the decision taken by the device 200.

As a variant, the calculation means 501, 502 and 503 of the border entity 51 could be shared with those of the device 200.

Referring to Figure 10, there is shown a server P-CSCF 52 according to the invention.

This P-CSCF server comprises a device 200 able to process a SIP response according to the invention and means 524 for sending a command to the entity C-BGF 53 of the core IMS network for this entity to start, stop or suspend the restitution of the preliminary flow by the calling terminal A according to the decision taken by the device 200. Application examples

The invention can be applied in several scenarios.

For example, a calling subscriber A who has subscribed to the permanent secret services calls a subscriber B.

This subscriber B has subscribed to an anonymous call screening service. It is also equipped with a terminal capable of broadcasting music in return call during the ring phase.

In this call configuration, the terminal A may be subject to two preliminary media streams during the ring phase: the music transmitted by the terminal of B and the message broadcast by the network which asks the caller to identify himself.

The mechanism proposed by the invention makes it possible to record, in an application server AS placed in a power outage between the calling terminal A and the called terminal, a priority scale so as not to restore in the handset of the user A that the preliminary media stream whose priority indicator is maximum.

The invention also makes it possible to resolve conflicts when several recipient terminals broadcast their own preliminary media stream in the case of a forking mechanism.

In an alternative embodiment of the invention, if the case in which a calling terminal receives two preliminary media streams with the same priorities occurs, a proprietary policy of the called terminal manufacturer could be implemented to choose, for example, the first or the last preliminary media stream received, the other streams being simply rejected. Alternatively, the operator can also choose to simultaneously render two preliminary media streams of the same priority, depending on the service logic implemented.

ANNEX 1

REP:

183 Call in Progress

F rom: A@operator.com; tag = 1234

To: B@operator.com; tag = Btotag

Cseq: 5678 INVITE

P-early-Media: sendonly; Media-Priority = 100

Content-type: application / sdp

SDP

ANNEX2

REP:

183 Call in Progress

F rom: A@operator.com; tag = 1234

To: B@operator.com; tag = Btotag

Cseq: 5678 INVITE

Media-Priority = 100

P-Early-Media ...

Content-type: application / sdp

SDP

Claims

A method implemented by a called terminal (59, B) in an IMS network, said method comprising:

a step (E10) for receiving an INVITE SIP message sent by a calling terminal (A) to establish a communication between said terminals; and

- prior to a possible establishment of said communication, a step (E30) of sending a SIP response type 18x (REP) for informing said calling terminal that said called terminal has been alerted, said response comprising an SDP message ( MSDP) having characteristics of a preliminary media stream that can be established between said calling terminal and said called terminal prior to establishing said communication;

said method being characterized in that it comprises:

a step (E20) of inserting, into said SIP response, a priority indicator (IND) of said preliminary media stream.

2. Device (100) that can be integrated in a first terminal (B, 59) comprising:

means (104) for receiving an INVITE SIP message sent by a calling terminal (A) for establishing a communication between said terminals; and

means (104) for sending, prior to any establishment of said communication, a SIP response of type 18x (REP) intended to inform said calling terminal that said first terminal has been alerted, said response comprising an SDP message (MSDP) having features of a preliminary media stream that may be established between said calling terminal and said first terminal prior to establishing said communication;

said device being characterized in that it comprises:

means (101, 102, 103) for inserting, in said SIP response, a priority indicator (IND) of said preliminary media stream.

Terminal (B) comprising a device according to claim 2.

An application server (59) having a device according to claim 2.

A computer program (PG1) comprising instructions for performing the steps of the method of claim 1 when said program is executed by a computer.

A recording medium (103) readable by a computer on which a computer program (PG1) is recorded including instructions for performing the steps of the method according to claim 1.

A method of processing an 18x SIP response (REP) transmitted by a called terminal (B, 59) to a calling terminal (A), said response comprising an SDP message (MSDP) including a preliminary media stream that can be established between said calling terminal and said called terminal before establishing communication between these terminals, said method comprising:

a step (F10) of obtaining, in said SIP response, a priority indicator of said preliminary media stream; and

a decision step (F20) for authorizing, blocking or suspending the rendering of said preliminary media stream by said calling terminal according to said priority indicator.

8. Device (200) for processing an 18x SIP response sent by a called terminal (B, 59) to a calling terminal (A), said answer comprising an SDP message comprising characteristics of a stream preliminary media capable of being established between said calling terminal and said called terminal before the establishment of a communication between these terminals, said device comprising:

means (201, 202, 203) for obtaining, in said SIP response, a priority indicator of said preliminary media stream; and

means (201, 202, 203) for taking a decision as to the authorization, blocking or suspension of the rendering of said preliminary media stream by said calling terminal according to said priority indicator.

9. Terminal (A) comprising:

means (204) for sending an INVITE SIP message to a called terminal (B) this message being intended to establish a communication between said terminals; means (204) for receiving a SIP response type 18x (REP) transmitted by said called terminal, said answer comprising an SDP message (MSDP) comprising characteristics of a preliminary media stream that can be established between said terminals prior to establishment of said communication between these terminals;

said terminal being characterized in that it comprises:

a device (200) for processing said SIP response according to claim 8; and

control means (201, 202, 203) able to start, stop or suspend the rendering of said preliminary media stream by said terminal as a function of the decision taken by said device.

An entity (SBC) which can be placed in a flow-off between a calling terminal and a called terminal in an IMS network, said entity comprising:

means (504) for receiving a SIP response of type 18x (REP) sent by the called terminal (B) to the calling terminal (A), said response comprising an SDP message (MSDP) comprising characteristics of a preliminary media stream that can be established between said terminals before establishing said communication between these terminals;

said entity being characterized in that it comprises:

a device (200) for processing said SIP response according to claim 8; and

control means (501, 502, 503) able to start, stop or suspend the rendering of said preliminary media stream by said calling terminal as a function of the decision taken by said device.

11. Entity (SBC) according to claim 10, characterized in that it constitutes a bordering border entity between an access network (41) which is connected to said calling terminal and the IMS core network (40).

12. Server (52) having a visibility in the signaling plane, comprising:

means (524) for receiving a type 18x SIP response sent by said called terminal to a calling terminal, said answer comprising an SDP message comprising characteristics of a preliminary media stream that can be established between said terminals before establishing a communication between these terminals, said server being characterized in that it comprises:

a processing device (200) of said response according to claim 8; and

means (524) for sending a command to an entity (53) having visibility in the media plane for it to start, stop or suspend the rendering of said preliminary media stream by said calling terminal according to the decision made by said device.

Application server (59) comprising:

means (524) for receiving a type 18x SIP response sent by said called terminal to a calling terminal, said answer comprising an SDP message comprising characteristics of a preliminary media stream that can be established between said terminals before establishing a communication between these terminals,

said application server (59) being characterized in that it comprises:

a processing device (200) of said response according to claim 8; and

means for modifying, if necessary, the value of the priority indicator of a preliminary media stream in accordance with a predetermined service logic.

A computer program (PG2) comprising instructions for performing the steps of the method of processing a response according to claim 7 when said program is executed by a computer.

15. A computer-readable recording medium (203) on which is recorded a computer program comprising instructions for executing the steps of the method of processing a response according to claim 7.

16. Signal (GIS) intended to be transmitted by a called terminal to a calling terminal in an IMS network, this signal carrying a SIP response type 18x for informing said calling terminal that said called terminal has been alerted, said response comprising an SDP message (MSDP) comprising characteristics of a preliminary media stream that can be established between said calling terminal and said called terminal before the establishment of said communication;

said signal being characterized in that said SIP response includes a priority indicator (IND) of said preliminary media stream.

17. Signal according to claim 16, characterized in that said priority indicator is included in a header of said response reserved for this purpose.

18. Signal according to claim 16, characterized in that said priority indicator is a parameter of the P_EARLY_MEDIA header defined by the IETF RFC5009 standard.